And Theresa May, the Home Secretary, added to suggestions that senior cabinet ministers had not been consulted when she refused 11 times to reveal when she was told about the decision.

Mr Osborne's decision to abolish child benefit for higher-rate taxpayers met with controversy when it was announced on Monday, as experts claimed it unfairly penalised single-income families.

In an interview at a fringe event to the Conservative Party conference, Mr Duncan Smith appeared to suggest that journalists' interest in welfare reform had forced Mr Osborne into a premature announcement.

He said: "I think the reality is you were all spending your time just dwelling on this the whole time ... The reality is there was a sort of interest and that was why it was done."

When questioned repeatedly on BBC2's Newsnight on when she was informed, the Home Secretary would only say the decision was "a matter for the Chancellor and the Secretary of State for Work and Pensions".

David Davis, the senior backbencher, who was critical of the way the announcement was made, told the same programme that a "front bench rethink" was likely to take place.

He added: "When they work through the consequences of what they're proposing, they might think 'There's a better way of doing it'."

The growing questions over whether the policy was rushed through – some from within the Conservative party – forced senior Tories to defend their decision.

In a sign of the unease among Tories about a possible backlash from middle-class voters, Mr Osborne wrote to every Conservative MP on Tuesday explaining the rationale behind his decision.

David Cameron, the Prime Minister, apologised for leaving voters in the dark by omitting the cuts to the universal benefit from his general election manifesto, as the controversy threatened to overshadow his speech to the Conservative Party conference.

Mr Cameron is expected to justify the cuts to child benefit by insisting that it is "fair that those with broader shoulders should bear a greater load" in his speech on Wednesday.

William Hague, the foreign secretary, said on Wednesday morning that he had been aware the announcement was coming but did not give any further details on the extent to which it had been discussed prior to Mr Osborne's speech.

He added that the cuts for higher-rate taxpayers were "tough but fair".

Asked on the BBC Radio 4 Today programme if people facing cuts would just have to "lump it", he replied: "Yes, because this is a situation we have to deal with.

"Is this going to cause some people some pain? Yes, it is, but what alternative is there for the United Kingdom to rescue itself?"

Economic experts have called into question the fairness of the new child benefit framework, which penalises single-earner families where the breadwinner is paid £44,000 a year but allows households where two earners both pay the lower rate of tax to earn up to £87,000 without forfeiting their benefit.

The Institute of Fiscal Studies said after the announcement: "Some may think the proposed scheme is unfair because child benefit is withdrawn where an individual in a couple is a higher-rate taxpayer, regardless of the joint income of the couple."

John Whiting of the Chartered Institute of Taxation added: “Perhaps it wasn’t thought through. In many ways what we’re looking at are very valid things to debate but perhaps we should have had that debate earlier.”